BACKGROUND AND IMPORTANCE:: Formation of cerebral de novo aneurysms (CDNA) is rare, and pathogenesis remains obscure. We analyzed factors involved in formation of CDNA and suggest guidelines for follow-up of patients. CLINICAL PRESENTATION:: We retrospectively reviewed intracranial aneurysms at our institute and published reports from 1964 to 2008. Eleven patients were found with CDNA and 138 patients were collected from published literature. We assessed clinical characteristics, such as gender, size and site of CDNA, past history, and time to occurrence of CDNA. Of 11 patients, 10 were female and 1 was male; mean age of the first onset was 53 (25-69 years). Mean time between first aneurysms and CDNA was 10.6 (3-29 years). The most common site of occurrence was anterior circulation. One patient experienced contralateral occurrence, and 2 patients changed from anterior to posterior circulation CDNA. 6 (54.5%) patients had a history of arterial hypertension. Results from analysis of the whole series from the literature revealed that risk of rupture increased with previous history of hemorrhage. Contralateral occurrence of CDNA was related to previous location, and multiplicity, whereas occurrence of anterior to posterior changes of CDNA and shorter interval only correlated with an older age group. CONCLUSION:: Although formation of CDNA is rare, several factors may contribute to its occurrence. Female patients with a history of arterial hypertension were at a higher risk for CDNA occurrence. We recommend follow-up imaging studies within 10 years after the initial aneurysms; therefore, at least 50% of CDNA can be found before rupture.